1. Field of the Invention
The present invention relates to libraries of portable data storage media where different accessors move the media between various storage slots, read and/or write drives (xe2x80x9cread/writexe2x80x9d drives), and other access sites. More particularly, the invention concerns such a library in which different accessors are calibrated to different calibration locations in order to properly recognize different access sites associated with those locations. Even though a particular accessor might not be calibrated to reach certain sites, this accessor can still access those sites by using (1) calibration data of another accessor that has been calibrated to calibration locations associated with those sites, in conjunction with (2) a spatial relationship between the subject accessor and the other accessor.
2. Description of the Related Art
The media library is one popular apparatus for inexpensively managing a large volume of data. Depending upon the application, the portable media may comprise magnetic tape cartridges, optical media cartridges, and the like. Different accessors, such as robotic arms or horizontally/vertically sliding grippers, move the media between various storage slots, read/write drives, and other access sites.
Presently, there are a number of dual accessor data storage libraries in production. Dual accessors complete storage tasks more quickly since they can share workload. They also provide redundancy in case one accessor fails. As with any library, whether dual or single accessor, calibration is an important step in setting up and operating the library. Namely, the library includes certain predesignated physical points and other such xe2x80x9ccalibration locations,xe2x80x9d which have a given relationship to storage slots, read/write drives, and other access sites in the library. Each accessor is independently calibrated to all of the calibration locations. In one example, the calibration locations comprise small reflective areas, and the accessors physical situs of the calibration locations by emitting and detecting reflection of a small spot of light. Once the calibration location is obtained, the accessor notes the (x,y) coordinate or other position reading of the calibration location, completing calibration for this calibration location. In some cases, accessors locate numerous calibration locations and interpolate between them to find an intermediate point.
Although the foregoing arrangements are satisfactory in many respects, engineers at International Business Machines Corp. (xe2x80x9cIBMxe2x80x9d) are continually seeking to improve the performance and efficiency of dual accessor media libraries. In this respect, IBM engineers have recognized one potential limitation, in that calibration can be time consuming. In a large library, for instance, calibration can take nearly twenty minutes. With larger libraries, calibration is even more time consuming. Library performance definitely suffers during calibration, since the library is unable to access customer data during that time. Another potential limitation with dual accessor libraries is that valuable storage is occupied by the empirically determined coordinates of all calibration locations in the library as independently determined by each accessor. Furthermore, this storage space is doubled if the calibration data is backed up. In addition, managing data for the two accessors can be cumbersome, especially when managing backup data for each accessor.
Accordingly, the performance and efficiency of today""s dual accessor libraries suffers due to the length of calibration time, and also due to the storage occupied by calibration data.
A portable data storage media library includes multiple accessors, various designated access sites, and multiple calibration locations having predetermined spatial relationships to the access sites. Initially, the accessors are physically calibrated to various calibration locations such that each calibration location has at least one accessor calibrated thereto (except for any calibration locations that are inactive, irrelevant to the current library configuration, or otherwise unused). Moreover, each accessor is physically calibrated to at least one calibration location in common with at least one other accessor. Next, physical calibration information is shared among the accessors. Each accessor then processes shared physical calibration information from other accessors to logically calibrate that accessor to all calibration locations for which the accessor has not been physically calibrated.
The invention affords its users with a number of distinct advantages. For example, multi-accessor calibration time can be significantly reduced by sharing the burden of calibration among accessors operating in parallel. Additionally, in one embodiment where some common calibration data is shared among the accessors, the overall volume of calibration data is reduced, preserving data storage space. The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.